1911 Encyclopædia Britannica/Copal
COPAL (Mexican copalli, incense), a hard lustrous resin, varying in hue from an almost colourless transparent mass to a bright yellowish-brown, having a conchoidal fracture, and, when dissolved in alcohol, spirit of turpentine, or any other suitable menstruum, forming one of the most valuable varnishes. Copal is obtained from a variety of sources; the term is not uniformly applied or restricted to the products of any particular region or series of plants, but is vaguely used for resins which, though very similar in their physical properties, differ somewhat in their constitution, and are altogether distinct as to their source. Thus the resin obtained from Trachylobium Hornemannianum is known in commerce as Zanzibar copal, or gum animé. Madagascar copal is the produce of T. verrucosum. From Guibourtia copallifera is obtained Sierra Leone copal, and another variety of the same resin is found in a fossil state on the west coast of Africa, probably the produce of a tree now extinct. From Brazil and other South American countries, again, copal is obtained which is yielded by Trachylobium Martianum, Hymenaea Courbaril, and various other species, while the dammar resins and the piney varnish of India are occasionally classed and spoken of as copal. Of the varieties above enumerated by far the most important from a commercial point of view is the Zanzibar or East African copal, yielded by Trachylobium Hornemannianum. The resin is found in two distinct conditions: (1) raw or recent, called by the inhabitants of the coast sandarusiza miti or chakazi, the latter name being corrupted by Zanzibar traders into “jackass” copal; and (2) ripe or true copal, the sandarusi inti of the natives. The raw copal, which is obtained direct from the trees, or found at their roots or near the surface of the ground, is not regarded by the natives as of much value, and does not enter into European commerce. It is sent to India and China, where it is manufactured into a coarse kind of varnish. The true or fossil copal is found embedded in the earth over a wide belt of the mainland coast of Zanzibar, on tracts where not a single tree is now visible. The copal is not found at a greater depth in the ground than 4 ft., and it is seldom the diggers go deeper than about 3 ft. It occurs in pieces varying from the size of small pebbles up to masses of several ounces in weight, and occasionally lumps weighing 4 or 5 ℔ have been obtained. After being freed from foreign matter, the resin is submitted to various chemical operations for the purpose of clearing the “goose-skin,” the name given to the peculiar pitted-like surface possessed by fossil copal. The goose-skin was formerly supposed to be caused by the impression of the small stones and sand of the soil into which the soft resin fell in its raw condition; but it appears that the copal when first dug up presents no trace of the goose-skin, the subsequent appearance of which is due to oxidation or inter-molecular change.